1. Technical Field
Exemplary aspects of the present disclosure generally relate to a belt tracking system, a roller assembly, and an image forming apparatus employing the same, and more particularly, to a belt tracking system for adjusting misalignment of a movable belt in an axial direction of a plurality of rollers about which the movable belt is entrained, and a roller assembly, and an image forming apparatus employing the belt tracking system.
2. Description of the Related Art
Known image forming apparatuses employ various types of movable imaging belts, such as an intermediate transfer belt, a media conveyor belt, and a fixing belt, each of which is entrained about a plurality of generally parallel support rollers and rotated by the rotation of the rollers. Due to wear and tear of parts used to rotate the belt support rollers, the belt support rollers are no longer aligned parallel to each other. Furthermore, because multiple parts are connected, the parts vary from one to another and variation among these parts can cause a different degree of connection at the left end and the right end of the rollers. As a result, the belt support rollers are not aligned parallel.
When these rollers are no longer parallel, the belt runs over the rollers in the axial direction of the rollers, resulting in breakage of the belt.
To address this difficulty, several techniques have been proposed which employ a belt tracking system to correct the position of the belt which has drifted in the axial direction of the roller. For example, there is known a belt tracking system in which a rotary member with an inclined surface and a stationary guide member are provided to correct displacement of the belt. Such a configuration is proposed in JP-2009-288426-A.
In order to facilitate an understanding of the related art and of the novel features of the present invention, with reference to FIGS. 10A and 10B, a description is provided of a known belt tracking system to correct displacement of the belt. As illustrated in FIG. 10A, the belt tracking system includes a roller 91 about which a sheet conveyor belt 90 is entrained, rotary members 92a and 92b including inclined surfaces 93a and 93b, respectively, and stationary guide members 94a and 94b that contact the inclined surfaces 93a and 93b, respectively. FIG. 10A illustrates the sheet conveyor belt 90 without skew. As illustrated in FIG. 10A, when the sheet conveyor belt 90 is in its proper operational position without skew, the rotary members 92a and 92b at both ends in the axial direction of the roller 91 contact the stationary guide members 94a and 94b, respectively.
By contrast, as illustrated in FIG. 10B, when the sheet conveyor belt 90 drifts to one side, the belt edge contacts and presses against one of the rotary members 92a and 92b in the axial direction, causing the pressed rotary member 92a (or 92b) to move in the direction of skew of the belt 90 (in this example, the rotary member 92a is pressed to the right side of the drawing). As a result, as illustrated in FIG. 10B, the inclined surface 93a of the rotary member 92a at one axial end of the roller 91 contacts the stationary guide member 94, causing the roller 91 at that axial end to tilt downward. The end of the roller 91 at the rotary member 92a side tilts downward, thereby moving the sheet conveyor belt 90 in a direction opposite the direction of skew and hence correcting the position of the sheet conveyor belt 90.
According to JP-2009-288426-A, the end of the roller 91 at the rotary member 92a side tilts downward as described above, separating from the stationary guide member 94 as illustrated in FIG. 10C and hence hindering proper rotation of the roller 91.
To address such difficulty, in JP-2009-18691-A, a roller shaft support 96 (shown in FIG. 10D) including an elastic member 96f such as a spring or the like is provided to each of the rotary members 92a and 92b so as to exert force thereto towards the stationary guide members 94a and 94b, respectively. FIG. 10D illustrates the roller shaft support 96 provided to the belt tracking system of FIG. 10A. FIG. 11 illustrates the belt tracking system of FIG. 10D as viewed from an axial direction Z. As illustrated in FIG. 11, the known belt tracking system includes the roller shaft support 96 having a main body 96d to surround the roller 91. The main body 96d rotates about a center or hinge 96a in a direction of arrow R1 when the roller 91 and the rotary member 92a (92b) move down, thereby compressing the elastic member 96f. 
In this state, the restorative force of the elastic member 96f in a direction of arrow R2 acts on the main body 96d, moving the rotary member 92a (92b) and the roller 91 in the direction of arrow R2. As a result, the rotary body 92a (92b) remains in contact with the stationary guide member 94, thereby reliably rotating the roller 91.
In another approach, JP-H06-51646 proposes rotating the roller shaft support 96 that supports a roller such as the roller 91 as illustrated in FIG. 12. By rotating the roller shaft support 96, a circumference of a circle constituted by each roller can be made significantly shorter than an inner circumference of the belt 90, thereby facilitating removal of the belt 90 from the rollers.
Although advantageous, with the belt tracking system including the roller shaft support 96 with the elastic member 96f, attachment and detachment of the belt 90 may be difficult with respect to the image forming apparatus.
FIG. 13 illustrates the roller shaft support 96 including the elastic member 96f in the known belt tracking system when the roller shaft support 96 is rotated. FIG. 14 is a perspective view schematically illustrating the known belt tracking system shown in FIG. 13. As illustrated in FIG. 13, when the roller shaft support 96 rotates about a rotary shaft 96g, the belt 90 is caught by the elastic member 96f upon removal and installation of the belt 90 as shown in FIG. 14.